Through petrological and mineral chemistry studies of the mafic hydrous phases of the Proterozoic quartz syenites along the NE margin of Cuddapah Intrusive Province (CIP) of the Eastern Dharwar Craton (EDC), we present the nature of the magmatic sources of the Mesoproterozoic Purimetla quartz syenite (PUQS) and the Vikurthi and Kottappakonda quartz syenites (VKQS). Earlier studies suggested that these rocks evolved from subalkaline magmas. However, the present study, based on amphibole and biotite mineral chemistry, demonstrates the contrasting magmatic sources of the PUQS and VKQS. Results of electron probe micro-analyzer (EPMA) chemical analyses indicate that the calcium amphiboles in the PUQS are ferro-pargasite-hastingsite and edenite in the VKQS. Biotite is Fe-rich (annite) in the PUQS and Mg-rich (phlogopite affinity) in the VKQS. Bulk rock, amphibole, and biotite geochemical ratios [e.g. MgO/(FeO^T + MgO); with FeO^T = total Fe oxide assuming all Fe to be Fe²⁺] demonstrate the ferroan (PUQS) and magnesian (VKQS) nature of the respective magmas. Though both the plutons show variations in SiO₂, FeO, MgO, and CaO contents, they present similarities in total alkalies. The mineral chemistry of the mafic hydrous minerals indicates the alkaline nature of PUQS and the subalkaline nature of the VKQS magmas. Temperature estimates for the crystallization of the PUQS and VKQS, based on amphibole Al₂O₃ and TiO₂ contents, are 840–800 °C and 780–650 °C respectively. Lower-temperature estimates were obtained for the crystallization of biotite in the PUQS (760–730 °C) and VKQS (730–650 °C). Overall pressure estimates, based on Al in hornblende barometry, suggest that the PUQS formed at ~ 6–9 kbar and the VKQS at ~ 3– 6 kbar. Furthermore, the oxygen fugacity (fO₂) estimates derived from amphibole chemistry suggest reduced conditions of crystallization for the PUQS and oxidized conditions for the VKQS. Likewise, the fO₂ estimates using biotite Fe²⁺, Fe³⁺, and Mg contents also indicate reduced conditions for the PUQS (close to the QFM – quartz-fayalite-magnetite buffer) and oxidized conditions for the VKQS (NNO – nickel-nickel oxide buffer). Based on bulk-rock and mineral chemistry data integration, we envisage that the PUQS evolved from anorogenic alkaline magmas, while the VKQS evolved from an orogenic, calc-alkaline to subalkaline magmas. Finally, the thermobarometric data (amphibole and biotite) for the two quartz syenites correspond to a lower crustal level crystallization for the PUQS (~ 30 km) and upper crustal level crystallization for the VKQS (10–15 km).

通过对东达瓦尔克拉通 (EDC) 库达帕侵入省 (CIP) 东北缘元古代石英正长岩的基性水相的岩石学和矿物化学研究，我们展示了中元古代普里梅特拉石英正长岩的岩浆来源的性质(PUQS) 和 Vikurthi 和 Kottappakonda 石英正长岩 (VKQS)。早期的研究表明，这些岩石是由亚碱性岩浆演化而来的。然而，本研究基于闪石和黑云母矿物化学，证明了 PUQS 和 VKQS 的对比岩浆来源。电子探针显微分析仪 (EPMA) 化学分析结果表明，PUQS 中的钙闪石是铁-磷灰石-黑晶石和 VKQS 中的钙长石。黑云母在 PUQS 中富含铁（长石），在 VKQS 中富含镁（金云母亲和力）。块状岩石，^T  + MgO); 其中 FeO ^T  = 总氧化铁，假设所有的 Fe 都是 Fe ²⁺ ] 证明了各自岩浆的铁质 (PUQS) 和镁质 (VKQS) 特性。_{尽管两个岩体在 SiO 2}、FeO、MgO 和 CaO 含量方面都表现出变化，但它们在总碱中表现出相似性。镁铁质含水矿物的矿物化学表明 PUQS 的碱性性质和 VKQS 岩浆的亚碱性性质。基于闪石 Al ₂ O ₃和 TiO _{2的 PUQS 和 VKQS 结晶温度估算}含量，分别为 840–800 °C 和 780–650 °C。获得了 PUQS（760-730 °C）和 VKQS（730-650 °C）中黑云母结晶的较低温度估计值。基于角闪石气压计中的铝的总压力估计表明，PUQS 形成于 ~ 6-9 kbar，VKQS 形成于 ~ 3-6 kbar。此外，来自闪石化学的氧逸度 ( f O ₂ ) 估计表明 PUQS 的结晶条件降低，而 VKQS 的氧化条件则降低。同样，使用黑云母 Fe ²⁺、 Fe ^3+的f O ₂估计值和 Mg 含量也表明 PUQS 的还原条件（接近 QFM - 石英-铁橄榄石 - 磁铁矿缓冲液）和 VKQS 的氧化条件（NNO - 镍-氧化镍缓冲液）。基于大块岩石和矿物化学数据整合，我们设想 PUQS 从造山碱性岩浆演化而来，而 VKQS 从造山带钙碱性岩浆演化为亚碱性岩浆。最后，两种石英正长岩的热气压数据（闪石和黑云母）对应于 PUQS 的下地壳水平结晶（~30 km）和 VKQS 的上地壳水平结晶（10-15 km）。